$split (aggregation)¶

Definition定义¶

$split¶

Divides a string into an array of substrings based on a delimiter. 基于分隔符将字符串划分为子字符串数组。$split removes the delimiter and returns the resulting substrings as elements of an array. $split删除分隔符并将结果子字符串作为数组元素返回。If the delimiter is not found in the string, $split returns the original string as the only element of an array.如果在字符串中找不到分隔符，$split将原始字符串作为数组的唯一元素返回。

$split has the following operator expression syntax:$split具有以下运算符表达式语法：

{ $split: [ <string expression>, <delimiter> ] }

Field字段	Type类型	Description描述
string expression	string	The string to be split. 要拆分的字符串。string expression can be any valid expression as long as it resolves to a string. string expression可以是任何有效的表达式，只要它解析为字符串。For more information on expressions, see Expressions.有关表达式的详细信息，请参阅表达式。
delimiter	string	The delimiter to use when splitting the string expression. 拆分字符串表达式时使用的分隔符。delimiter can be any valid expression as long as it resolves to a string.delimiter可以是任何有效的表达式，只要它解析为字符串。

Behavior行为¶

The $split operator returns an array. $split运算符返回一个数组。The <string expression> and <delimiter> inputs must both be strings. <string expression>和<delimiter>输入必须都是字符串。Otherwise, the operation fails with an error.否则，操作将失败并出现错误。

{ $split: [ "June-15-2013", "-" ] }

[ "June", "15", "2013" ]

{ $split: [ "banana split", "a" ] }

[ "b", "n", "n", " split" ]

{ $split: [ "Hello World", " " ] }

[ "Hello", "World" ]

{ $split: [ "astronomical", "astro" ] }

[ "", "nomical" ]

{ $split: [ "pea green boat", "owl" ] }

[ "pea green boat" ]

Example示例¶

A collection named deliveries contains the following documents:名为deliveries的集合包含以下文档：

{ "_id" : 1, "city" : "Berkeley, CA", "qty" : 648 }
{ "_id" : 2, "city" : "Bend, OR", "qty" : 491 }
{ "_id" : 3, "city" : "Kensington, CA", "qty" : 233 }
{ "_id" : 4, "city" : "Eugene, OR", "qty" : 842 }
{ "_id" : 5, "city" : "Reno, NV", "qty" : 655 }
{ "_id" : 6, "city" : "Portland, OR", "qty" : 408 }
{ "_id" : 7, "city" : "Sacramento, CA", "qty" : 574 }

The goal of following aggregation operation is to find the total quantity of deliveries for each state and sort the list in descending order. It has five pipeline stages:下面的聚合操作的目标是找到每个状态的交付总量，并按降序对列表进行排序。它有五个管道阶段：

• The $project stage produces documents with two fields, qty (integer) and city_state (array). $project阶段生成包含两个字段的文档：qty（整数）和city_state（数组）。The $split operator creates an array of strings by splitting the city field, using a space (" ") as a delimiter.$split运算符通过使用空格（" "）作为分隔符拆分city字段来创建字符串数组。
• The $unwind stage creates a separate record for each element in the city_state field.$unwind阶段为city_state字段中的每个元素创建单独的记录。
• The $match stage uses a regular expression to filter out the city documents, leaving only those containing a state.$match阶段使用正则表达式筛选城市文档，只留下那些包含州的文档。
• The $group stage groups all the states together and sums the qty field.$group阶段将所有状态组合在一起，并对qty字段求和。
• The $sort stage sorts the results by total_qty in descending order.$sort阶段按总数量降序对结果进行排序。

db.deliveries.aggregate([
  { $project : { city_state : { $split: ["$city", ", "] }, qty : 1 } },
  { $unwind : "$city_state" },
  { $match : { city_state : /[A-Z]{2}/ } },
  { $group : { _id: { "state" : "$city_state" }, total_qty : { "$sum" : "$qty" } } },
  { $sort : { total_qty : -1 } }
]);

The operation returns the following results:操作返回以下结果：

{ "_id" : { "state" : "OR" }, "total_qty" : 1741 }
{ "_id" : { "state" : "CA" }, "total_qty" : 1455 }
{ "_id" : { "state" : "NV" }, "total_qty" : 655 }